Si-TiN alloy Li-ion battery negative electrode materials made by N 2 gas milling
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Research Letter
Si–TiN alloy Li-ion battery negative electrode materials made by N2 gas milling Y. Wang, Department of Chemistry, Dalhousie University, Halifax, N.S. B3H 4R2 Canada; School of Materials Science and Engineering and Key Laboratory of Advanced Energy, Storage Materials of Guangdong Province, South China University of Technology, Guangzhou 510641, P. R. China Simeng Cao, Department of Chemistry, Dalhousie University, Halifax, N.S. B3H 4R2 Canada Hui Liu, Department of Chemistry, Dalhousie University, Halifax, N.S. B3H 4R2 Canada; School of Materials Science and Engineering and Key Laboratory of Advanced Energy, Storage Materials of Guangdong Province, South China University of Technology, Guangzhou 510641, P. R. China Min Zhu, School of Materials Science and Engineering and Key Laboratory of Advanced Energy, Storage Materials of Guangdong Province, South China University of Technology, Guangzhou 510641, P. R. China M.N. Obrovac, Department of Chemistry, Dalhousie University, Halifax, N.S. B3H 4R2 Canada; Department of Physics and Atmospheric Science, Dalhousie University, Halifax, N.S. B3H 4R2 Canada Address all correspondence to M.N. Obrovac at [email protected] (Received 5 June 2018; accepted 15 August 2018)
Abstract Si–TiN alloys are attractive for use as negative electrodes in Li-ion cells because of the high conductivity, low electrolyte reactivity, and thermal stability of TiN. Here it is shown that Si–TiN alloys with high Si content can surprisingly be made by simply ball milling Si and Ti powders in N2(g); a reaction not predicted by thermodynamics. This offers a low-cost and simple method of synthesizing these attractive materials. The resulting alloys have smaller grain sizes than Si–TiN made by ball milling Si and TiN directly, giving them high thermal stability and improved cycling characteristics in Li cells.
Introduction Si-based materials can store up to 2.8 times the amount of lithium per unit volume as graphite, making them highly attractive for use as the negative electrode in Li-ion batteries.[1,2] Si–TiN alloys for Li-ion battery negative electrodes were introduced by Kim et al. in 2000.[3] These alloys were made by high-energy ball milling Si and TiN powders in Ar(g). The cycling performance of Si(TiN)0.5 shown by Kim et al.[3] (1100 Ah/L, 20 cycles, no fade) was impressive for the time, especially considering that no advanced binders or electrolyte additives were used. This alloy composition combines high volumetric capacity Si with TiN, which is a metallic conductor. We have recently shown that TiN is also remarkably inert towards reactions with the electrolyte at the negative electrode.[4] These properties of TiN may contribute to the good performance of Si–TiN alloys reported by Kim et al. in Ref. 3. TiN also has a high melting point (∼3300°C),[5] which may confer high thermal stability to Si–TiN alloys. This could make them compatible to carbon coating by chemical vapor deposition (CVD), which has been shown to enhance alloy cycle life.[6] Unfortunately, industrial production
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